Wed, 22 Mar 2000 21:56:39 -0700, Allen wrote:
>From: Terry M. Gray <grayt@lamar.colostate.edu>
[Snipped Terry's 1st Paragraph]
>> But, what if, oh and it seems a big what if in the contemporary
>> discussion,
>> what if, you are a theist and a creationist (i.e. you believe that God
>> created), but you also believe that God could have created however he
>> pleased (including using evolutionary processes) and that you are willing
>> to let the evidence tell you how he did it (not your interpretation of
>> Genesis)??????
>
>The key here is; What is the evidence for evolution? We all acknowledge
>genetic variation, which might be called, in one sense, evolution. However,
>the evolution we are discussing here is the application of genetic variation
>over a long period of time resulting in the varieties of life forms that now
>exist. The evidence for this is interpreted from the fossil record and the
>interpretation of vast ages of the rocks. If the rocks are old then the
>fossils would represent a record of life over vast ages. Are the
>sedimentary rocks old? The results of radiometric dating are offered as
>evidence of the vast ages of the rocks.
>
>However, one of the axioms (or presuppositions) for radiometric dating is
>that the rocks are old enough to be dated. Thus one must first asume that
>the rocks are old before you can date them. Consequently, radiometric dates
>cannot provide evidence of the old age of the rocks because old age is
>already assumed in the dating method. You cannot prove what you assume.
Allen,
I don't have time to reply in detail to this entire post but I was enticed
out of my lurking mode by this "radiometric age dates" argument. I'll leave
the much anticipated discussion of Evolutionary Creationist's motives,
theology, etc for Terry ;^)
This is at least the second time that I have seen you make this argument for
circular reasoning in age dating. In a sense, you are correct. I assume
"that the rocks are old enough to be dated." I also assume that my
14-yr-old daughter is old enough to be dated ... in the sense that we can
assign an age to her, NOT in the sense in which she would prefer. The point
is that assuming an object is old enough for its age to be determined
doesn't invalidate the measured age. All I need is the right method.
But let's take this a little further. I'm assuming that your argument is
really that we (geologists) assume some igneous rock is in the neighborhood
of 1 billion yrs old and then we choose a radiometric method (like K-Ar,
Rb-Sr, U-Pb, Lu-Hf, Re-Os, or Sm-Nd) which will give us measurements in that
neighborhood. You are again correct ... in the sense that I would use an
instrument calibrated to thousandths of a second to time a 50-meter dash and
yet use another timepiece to determine the winning time of the Iditarod dog
sled race. Those chosen methods do not invalidate the measured age, they
just differ in their relative precision.
Let me throw out one piece of empirical evidence that suggests that we are
in the right ballpark when we try to date the oldest rocks in billions of
years rather than in the 6,000 to 10,000 yr range. For the 103 to 105 known
elements, there are in the neighborhood of 1,000 known isotopes, of which
perhaps 60-70% are unstable and decay radiometrically. The majority of
these radioactive isotopes have half-lifes on the order of a few
milleseconds to a few days. A small but significant number are measured in
years. Only a handfull have half-lifes greater than 1 million years. (These
numbers are guestimates that I've made from the Table of Isotopes found in
my 57th edition of the CRC Handbook of Chemistry and Physics (pages B-270 to
B354, 1976). Since they annually review and revise this 4" thick book, you
should be able to find a new version in any public library.)
With only a few exceptions, none of these radioactive isotopes with
half-lifes less than about 700 million years are found in nature.
Exception #1: Radioactive isotopes produced by the decay of
elements with half-lifes greater than 700 million years.
Exception #2: Radioactive isotopes produced by known and natural
processes like the production of Carbon-14 by sunlight
in the upper atmosphere.
Exception #3: Radioactive isotopes produced and released by man.
Since the average life expectancy of any radiometric isotope is on the order
of 10 times the half-life, we can reasonably infer that the elements of
which our earth is composed were created no less than about 1-7 billion
years ago.
Here is a table that was sent to me. I haven't checked all the numbers but
the few that I did agree with the data in the CRC Handbook. In the Y/N
column, a Y means that it is found naturally occurring, a N means that it
has not been found. An * means that the elements is produced by the decay of
another element with a half-life greater than 700 million years. Note that
Pu-244 is man-made plutonium that was probably released by nuclear testing.
Nuclide Halflife (Yrs) Y/N
V-50 6,000,000,000 M.Y. Y
Nd-144 2,400,000,000 M.Y. Y
Hf-174 2,000,000,000 M.Y. Y
Pt-192 1,000,000,000 M.Y. Y
In-115 600,000,000 M.Y. Y
Gd-152 110,000,000 M.Y. Y
Te-123 12,000,000 M.Y. Y
Pt-190 690,000 M.Y. Y
La-138 112,000 M.Y. Y
Sm-147 106,000 M.Y. Y
Rb-87 48,800 M.Y. Y
Re-187 43,000 M.Y. Y
Lu-176 35,000 M.Y. Y
Th-232 14,000 M.Y. Y
U-238 4,470 M.Y. Y
K-40 1,250 M.Y. Y
U-235 704 M.Y. Y
-------------
Pu-244 82 M.Y. Y
Sm-146 70 M.Y. N
Pb-205 30 M.Y. N
U-236 23.9 M.Y. Y*
I-129 17 M.Y. Y*
Cm-247 16 M.Y. N
Hf-182 9 M.Y. N
Pd-107 7 M.Y. N
Mn-53 3.7 M.Y. Y*
Cs-135 3 M.Y. N
Te-97 2.6 M.Y. N
Np-237 2.14 M.Y. N
Gd-150 2.1 M.Y. N
Be-10 1.6 M.Y. Y*
Zr-93 1.5 M.Y. N
Tc-98 1.5 M.Y. N
Dy-154 1 M.Y. N
Out of curiosity, I would like to see what the YEC position on this
empirical data is.
Steve
[The opinions expressed herein are my own
and are not to be attributed to my employer.]
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Steven M. Smith, Geologist Office: (303)236-1192
U.S. Geological Survey Fax: (303)236-3200
Box 25046, M.S. 973, DFC smsmith@usgs.gov
Denver, CO 80225
--The USGS National Geochemical Database NURE HSSR Data Web Site--
http://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-97-0492/
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